Patent GB-829994-A (GB)
Title: Improvements in and relating to electric control systems
Inventor: RUSSELL DEREK BARRY
IPC: B66B1/12
Filed: 1955-04-26
Abstract: 829,994. Controllers. ENGLISH ELECTRIC CO. Ltd. April 17, 1956 [April 26, 1955], No. 12009/5.5. Class 38 (3). A speed reference voltage for an electric motor driving a mine winder is developed across terminals 30, such voltage being determined by the position of inter-coupled sliding contacts 14, 15, as well as by the position of a sliding contact 13 controlled by a driver's lever 11. All the sliding contacts co-operate with a potentiometer 12 connected to a source 29 of constant potential. Limit stops 19, 20 confine the movement of the slider 13 to the lower half of the potentiometer. When the contacts 14, 15 are in the position shown, a resistor 26 is shunted across the upper half of the potentiometer 12 and the full speed reference voltage appears across the lower half of the potentiometer so that the driver may select any speed reference voltage up to the full speed value by setting the lever 11 in an appropriate position Movement of the contacts 14, 15 to their lowermost position causes the resistor 26 to be shunted across the lower half of the potentiometer whereby the driver is able to select any voltage up to the maximum creep speed value. Movement of the contacts 14, 15, in a downward direction does not alter the speed reference voltage until the slider 15 moves below the slider 13. During a forward winding operation, a cam follower 24 is biased by torque motor 24c so that roller 24a engages a cam wheel 25 which is driven by the winder. As the winding operation continues, a cam 25a causes rotation of the follower 24 to move the sliders 14, 15, downward. The cam 25a is so arranged that the sliding contacts 14, 15 reach their lowermost position when the mine cages are still a short distance from their landing positions. During the course of a reverse winding operation, the torque of the motor 24c is reversed whereby roller 24b engages cam wheel 25 and, afterwards, a cam 25b becomes effective for lowering the sliders 14, 15. The potentiometer may be of the face-plate type with the sliders 14, 15, mounted at opposite ends of an insulated arm for movement over two circles of studs. In such an arrangement, rotation of an operating shaft is adapted to move the sliding contacts, this shaft being coupled through speed-reducing gears to the cam follower, Fig. 2 (not shown). A pilot motor is also coupled to the shaft through a slipping clutch, and is energized temporarily, just after the beginning of each wind, to move the cam-follower to the fullspeed position. The cam-follower is subsequently returned to the maximum creepspeed position by the appropriate cam acting against the torque of the slipping clutch. In another arrangement, a selector switch is operated by the shaft for connecting the shunting resistor 26 across either the upper half or the lower half of the potentiometer. The selector switch may be operated in accordance with the positions of the conveyances driven by the winder motor. The sliding contacts 14, 15 may be moved by the winder-driven cam gearduring both the acceleration and deceleration periods of the wind.